The invention relates to an arrangement for the hydraulic operating of two clutches mounted in an all-wheel transmission line of a motor vehicle, the first clutch serving as a separating clutch in the transmission line to a first vehicle axle, the second clutch serving as the locking clutch for the blocking of a locking system by means of which the second vehicle axle, as a function of the rotational speed difference, can be connected between the two vehicle axles.
In the German Patent Document DE-PS 32 12 495, a hydraulic operation of a multi-plate clutch is described in which a differential gearing in the transmission line of a motor vehicle can be locked. For this purpose, a hydraulic piston, which is acted upon by pressure and by way of an engaging bearing on the interior, acts upon a diaphragm spring which is supported in the housing on the outer edge. A pressure piece guided in the housing rests against the diaphragm spring. When the diaphragm spring is braced, the plates can be brought into frictional engagement with the pressure piece.
An object of the present invention is to provide a clutch operation for an all-wheel drive of the above-mentioned type which requires little space and permits a safe operation of the motor vehicle even when the electronic all-wheel control fails or is impaired.
This and other objects are achieved by an arrangement for operating two clutches mounted in an all-wheel transmission line of a motor vehicle that has first and second vehicle axles, the arrangement comprising a separating clutch in the transmission line to the first vehicle axle, and a locking clutch for the blocking of a locking system by which the second vehicle axle is connected as a function of the rotational speed difference of the first and second vehicle axles. A first spring biases the separating clutch, while a second spring biases the locking clutch. A first hydraulic piston is coupled to the separating clutch and closes the separating clutch against the force of the first spring. A second hydraulic piston is coupled to the locking clutch and opens the locking clutch against the force of the second spring.
Since a locking clutch is provided, which is used for the blocking of the locking system for the front axle and which is held in the closed position by means of a spring, the locking clutch can be opened only by the application of hydraulic pressure. Even in the case of a failure of the all-wheel function, the front axle is therefore driven by means of a purely mechanical connection. In this case, the separating clutch to the rear axle is open and the drive to the rear axle is stopped. This is an important prerequisite for an ABS-system to become effective and for a stable driving operation also during braking.
In an advantageous embodiment of the present invention, two hydraulic pistons are provided as the hydraulic operating device. These hydraulic pistons are concentric with respect to one another and are guided in one another in a sealed manner so that an extremely space-saving construction is achieved.
Other objects, advantages and novel features of the present invention ill become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.